Reply to “Questionable Utility of Galactomannan Testing for Diagnosis of Exserohilum rostratum Infection”

REPLY

We thank Suwantarat and collaborators (1) for their interest in our work. The authors found low levels of galactomannan (GM) in an undiluted extract of Exserohilum rostratum isolated from an index patient related to the contaminated methylprednisolone acetate injection outbreak compared with levels in an Aspergillus fumigatus positive control. Although the difference might simply be attributed to strain variation, different fungal extraction methods may also explain the varying results. We used YPD (yeast extract-peptone-dextrose, 2:2:2 g/liter) broth medium, whereas Suwantarat et al. used Sabouraud dextrose broth. These media differ in both the concentrations of their ingredients and their pHs (6.5 versus 5.7). Medium pH may affect enzymatic activities such as those responsible for GM synthesis, as well as antigen-antibody interaction in the GM test. We suggest testing GM levels of E. rostratum extract from the index patient using both extraction methods. We agree that since cerebrospinal fluid from three outbreak patients tested negative by the GM assay, its role in the current outbreak might be limited. However, a conclusion regarding its role in the diagnosis of E. rostratum infection in general should await the publication of findings on additional cases, preferably of studies including testing of isolates of the organism.